1. Field of the Invention
The present invention relates to a vehicle entertainment system, and more particularly, to an in-flight entertainment system that delivers video, audio, and application software to passenger seats using a modulated radio-frequency (RF) signal having a plurality of channels.
2. Description of the Related Art
A conventional in-flight entertainment system typically employs a single RF cable to deliver video signals to the passenger seats. To deliver different video signals over multiple channels so that passengers can be provided with viewing choices, a video modulator is used. In a typical arrangement, the video modulator is connected to multiple video cassette players that generate a plurality of different NTSC video streams. The video modulator receives these video streams and modulates each different NTSC video stream into a frequency band corresponding to one of the multiple channels.
In the above-described system, each passenger seat is equipped with a seat controller card (SCC) that is tunable to the frequency bands corresponding to the multiple channels. Once the seat controller card is tuned to receive at a particular frequency band, it demodulates the RF signal received and sends the demodulated signal to a seat display unit for viewing.
Each seat controller card operates under the control of an application program that is downloaded from a system controller, that is commonly referred to as a cabin file server (CFS), but is loaded and run locally at its corresponding passenger seat location. The download path between the cabin file server and the passenger seat location includes the same video modulator and RF cable that are used to distribute the modulated NTSC video streams. The download process is illustrated in FIG. 1.
At the start of this process, preliminary messages are transmitted back and forth from the seat controller card and the cabin file server over an ARCNET network, which is a token passing bus using RS-485 protocol. First, the seat controller card requests an application software from the cabin file server, and the cabin file server replies with a file identifier associated with the requested application software. The seat controller card then requests a download using the file identifier, and the cabin file server responds with an acknowledgment and a message to xe2x80x9cprepare for download.xe2x80x9d
The download of data occurs over a download line connecting the cabin file server and the video modulator, and the single RF cable. First, the application program is retrieved by the cabin file server from its storage device, supplied to the video modulator in a synchronous data stream over the download line, modulated into a frequency band corresponding to one of the multiple channels of the video modulator, and distributed in common to the seat controller cards over the single RF cable. Then, the seat controller cards tune to the frequency band corresponding to the channel in which the application software is carried, demodulate the received RF signal, and load the application software into their resident memory for execution.
The conventional in-flight entertainment system described above operates adequately when the requests from the seat controller cards to download the application software are synchronized, i.e., when the requests are made substantially at the same time. However, when one of the requests is not synchronized with the others, that request will have to wait until the application software has finished downloading before it can start downloading another copy of the application software.
A partial solution to the above problem is to establish a time window of a predetermined length, e.g., 500 msec in FIG. 1, to provide the late requestor a 500 msec time window of opportunity to issue its request. However, as noted, this is only a partial solution in that requests made after this time window must still wait before it can start downloading.
Another limitation of the above-described system is that, once the cabin file server processor begins processing the download request, it must do so continuously until the downloading is complete. This is because the seat controller card uses for its inputs a synchronous protocol, known as HDLC (High Level Data Link Control which implements layer 2 of the OSI model), and requires the data stream generated by the cabin file server to be continuous. As a result, the cabin file server processor is required to continuously, without breaks, transmit data into its download line from beginning of the transmission to the end of the transmission, and has reduced flexibility in performing other tasks in parallel with the download process.
Also, when multiple requests for download are made by the seat controller cards at different times, the cabin file server processor is unable to accommodate these requests in parallel. It must queue the requests and execute them one by one. When this happens, the cabin file server processor becomes continually burdened with downloading tasks, leaving it less processing power to handle other tasks.
An object of the invention is to provide a vehicle entertainment system that distributes an executable program in more than one channel of a modulated RF signal. This resolves the download synchronization problems because an executable program may be accessed at two different times by different passenger seats.
Another object of the invention is to provide a vehicle entertainment system having multiple download lines between the cabin file server and the video modulator. By having multiple download lines, a passenger seat that missed the time window for downloading an executable program is permitted to request and download the executable program even before the first download has completed. The multiple download lines provides an additional advantage of permitting downloads of different executable programs to take place at the same time.
Still another object of the invention is to provide a vehicle entertainment system having a dedicated download processor and a buffer. The dedicated download processor is provided to reduce the processing load of the main processor, in particular, to take over the task of generating a continuous stream of data responsive to a download request and supplying them to the video modulator. The buffer provides the dedicated download processor an area where previously retrieved executable program may be stored for subsequent fast access.
Still a further object of the invention is to provide a vehicle entertainment system having an executable program stored in a MPEG-format that is subjected to a quadrature amplitude modulation before it is downloaded to the video modulator. The MPEG compression and the quadrature amplitude modulation permit multiple executable programs to be carried on a single channel of the RF modulated signal. This has the effect of dividing a single channel of the RF modulated signal into a plurality of sub-channels, so if the same executable program is carried in more than one sub-channel in a time-staggered manner, the download requests of this program can be fulfilled at different times. Further, since the sub-channels may contain different executable programs, the MPEG compression and the quadrature amplitude modulation provide an additional advantage of permitting downloads of different executable programs to take place at the same time.
Yet another object of the invention is to provide a method of managing download requests of executable programs in a vehicle entertainment system. In this method, a download buffer is examined to see if a requested program is stored therein. If it is, the requested program is retrieved from the download buffer using a dedicated download processor. This method improves the download speeds for subsequent download requests for the same executable program and frees up the main processor to handle other tasks.
Additional objects, features and advantages of the invention will be set forth in the description of preferred embodiments which follows.